Chemical vapor deposition reactor with preheating, reaction, and cooling zones

ABSTRACT

A vertical chemical vapor deposition (CVD) reactor and a method for synthesizing metal oxide impregnated carbon nanotubes. The CVD reactor includes a preheating zone portion and a reaction zone portion, and preferably an additional cooling zone portion and a product collector. The method includes (a) subjecting a liquid reactant solution comprising an organic solvent, a metallocene, and a metal alkoxide to atomization in the presence of a gas flow comprising a carrier gas and a support gas to form an atomized mixture, and (b) heating the atomized mixture to a temperature of 200° C.-1400° C., wherein the heating forms a metal oxide and at least one carbon source compound, wherein the metallocene catalyzes the formation of carbon nanotubes from the at least one carbon source compound and the metal oxide is incorporated into or on a surface of the carbon nanotubes to form the metal oxide impregnated carbon nanotubes.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of Ser. No. 15/077,600, nowallowed, having a filing date of Mar. 22, 2016.

BACKGROUND OF THE INVENTION Technical Field

The present disclosure relates to devices and methods for synthesizingmetal oxide impregnated carbon nanotubes. More specifically, the presentdisclosure relates to a chemical vapor deposition reactor and a methodfor synthesizing carbon nanotubes impregnated with metal oxideparticles.

Description of the Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, is neitherexpressly nor impliedly admitted as prior art against the presentinvention.

Impregnation of carbon nanotubes with metal or metal oxide nanoparticlesmay be performed by conventional methods, or by special techniques suchas microwave assisted impregnation (See S. C. Motshekga, S. K. Pillai,S. Sinha Ray, K. Jalama, and R. W. M. Krause, “Recent Trends in theMicrowave-Assisted Synthesis of Metal Oxide Nanoparticles Supported onCarbon Nanotubes and Their Applications,” J. Nanomater., 2012, pp. 1-15,January 2012, incorporated herein by reference in its entirety). Theconventional impregnation methods, such as electro-less deposition,physical evaporation, capillary action, physisorption, solid statereaction, colloidal chemistry, and radiolysis, involve various stepsranging from a strong acid treatment to ultra-sonication. Frequently,the reduction of metal salts takes hours or days and the size and shapeof the metal or metal oxide nanoparticles cannot be controlledefficiently (See R. V. Hull, L. Li, Y. Xing, and C. C. Chusuei, “PtNanoparticle Binding on Functionalized Multiwalled Carbon Nanotubes,”Chem. Mater., vol. 18, no. 7, pp. 1780-1788, April 2006, B. Xue, P.Chen, Q. Hong, J. Lin, and K. L. Tan, “Growth of Pd, Pt, Ag and Aunanoparticles on carbon nanotubes,” J. Mater Chem., vol. 11, no. pp.2378-2381, January 2001. K. R. Reddy, K. P. Lee, A. I. Gopalan, M. S.Kim, A. M. Showkat, and Y. C. Nho, “Synthesis of metal (Fe or Pd)/alloy(Fe—Pd)-nanoparticles-embedded multiwall carbon nanotubes/sulfonatedpolyaniline composites by γ irradiation,” J. Polym. Sci. Part A Polym.Chem., vol. 44, no, 10, pp. 3336-1. May 2006. C. Mao, D. J. Solis, B. D.Reiss, S. T. Kottmann, R. Y. Sweeney, A. Hayhurst, G. Georgiou, B.Iverson, and A. M. Belcher, “Virus-based toolkit for the directedsynthesis of magnetic and semiconducting nanowires,” Science, vol. 303,no. 5655, pp. 213-7. January 2004. W. Q. Han and A. Zettl, “CoatingSingle-Walled Carbon Nanotubes with Tin Oxide,” Nano Lett., vol. 3, no.5. pp. 681-683, May 2003, each incorporated herein by reference in theirentirety).

On the other hand, microwave assisted impregnation methods are widelyused nowadays for chemical auctions and nano-material production,however, the methods are difficult to implement for impregnation ofcarbon nanotubes with metal or metal oxide nanoparticles (See W. X.Chen, J. Y. Lee, and Z. Liu, “Preparation of Pt and PtRu nanoparticlessupported on carbon nanotubes by microwave-assisted heating polyolprocess,” Mater. Lett., vol. 58, no. 25. pp. 3166-3169. October 2004. Q.C. Xu, J. D. Lin, J. Li, X. Z. Fu, Y. Liang, and D. W. Liao,“Microwave-assisted synthesis of MgO-CNTs supported ruthenium catalystsfor ammonia synthesis,” Catal. Commun., vol. 8, no. 12, pp. 1881-1885,December 2007. M. Nuchter, B. Ondruschka, W. Bonrath, and A. Gum,“Microwave assisted synthesis—a critical technology overview.” GreenChem., vol. 6, no. 3, p. 128, March 2004, each incorporated herein byreference in their entirety). The difficulty lies in the fact that inorder to transform a metal salt to a desired metal or a metal oxidecompound, a microwave of a specific wavelength is required.

Thus, it is an object of the present disclosure to provide a chemicalvapor deposition reactor and a method for synthesizing metal oxideimpregnated carbon nanotubes that is less time consuming and easier toperform as compared to the conventional and microwave assistedimpregnation methods.

BRIEF SUMMARY OF THE INVENTION

The present disclosure relates to a method of synthesizing carbonnanotubes impregnated with at least one metal oxide. The method includes(a) subjecting a liquid reactant solution to atomization in the presenceof at least one gas flow comprising at least one carrier gas and atleast one support gas, wherein the liquid reactant solution comprises atleast one organic solvent, at least one metallocene, and at least onemetal alkoxide, to form an atomized mixture comprising droplets of theliquid reactant solution and the at least one gas flow, and (b) heatingthe atomized mixture to a temperature of 200° C.-1400° C., wherein theheating forms at least one metal oxide and at least one carbon sourcecompound, wherein the at least one metallocene catalyzes the formationof carbon nanotubes from the at least one carbon source compound and theat least one metal oxide is incorporated into or on a surface of thecarbon nanotubes to form the carbon nanotubes impregnated with the atleast one metal oxide.

In one or more embodiments, the method further comprises collecting thecarbon nanotubes impregnated with the at least one metal oxide.

In one or more embodiments, the at least one carrier gas is at least oneselected from the group consisting of He, N₂, and Ar.

In one or more embodiments, the at least one support gas is selectedfrom the group consisting of CO₂, H₂O, H₂ and NH₃.

In one or more embodiments, the at least, one organic solvent isselected from the group consisting of 2-methoxy ethanol, 2-ethoxyethanol, 2-methoxy propanol, 2-ethoxy propanol, 2-propoxy propanol,2-butoxy propanol, 2-butoxy butanol, cyclohexane, heptane, octane,benzene, toluene, ethyl benzene, xylene, cumene, and styrene.

In one or more embodiments, the at least one metallocene is selectedfrom the group consisting of a metallocene of Ni, a metallocene of Co, ametallocene of Fe, a metallocene of Cr, a metallocene of Mo, ametallocene of Rh, a metallocene of Ti, a metallocene of W, ametallocene of V, and a metallocene of Zr.

In one or more embodiments, the at least one metal alkoxide is one ormore metal alkoxy alkoxides.

In one or more embodiments, the at least one metal alkoxide is selectedfrom the group consisting of an aluminum alkoxide, a titanium alkoxide,a magnesium alkoxide, a calcium alkoxide, a strontium alkoxide, a bariumalkoxide, a scandium alkoxide, a yytrium alkoxide, a zirconium alkoxide,a lanthanum alkoxide, a vanadium alkoxide, and a silicon alkoxide.

In one or more embodiments, the at least one metal alkoxide is aluminumisopropoxide which is heated to form aluminum oxide and the carbonnanotubes formed are multi-walled carbon nanotubes, and the synthesizedmulti-walled carbon nanotubes impregnated with the aluminum oxide have aBET surface area of 450-2000 m²/g.

In one or more embodiments, the at least one metal alkoxide is aluminumisopropoxide which is heated to form aluminum oxide, and 1-99 wt % ofthe aluminum oxide incorporated into or on the surface of the carbonnanotubes is in corundum phase.

Additionally, the present disclosure relates to a vertical chemicalvapor deposition reactor. The vertical chemical vapor deposition reactorincludes a preheating zone portion comprising a first enclosed chamberand having a top, a bottom, and sides with a wall defining the firstenclosed chamber; a first inlet located at the top of the preheatingzone portion for introducing carrier, support, and/or reactant gases andat least one liquid reactant solution into the first enclosed chamber;an ultrasonic atomizing nozzle operatively connected to the first inletfor releasing the carrier, support, and or reactant gases and the atleast one liquid reactant solution inside the first enclosed chamber; areaction zone portion comprising a second enclosed chamber and having atop connected to and in fluid communication with the bottom of thepreheating zone portion, a bottom, and sides with a wall defining thesecond enclosed chamber; a heater interposed between the top and thebottom of the reaction zone portion for heating the carrier, support,and/or reactant gases and the at least one liquid reactant solution; andan outlet at the bottom of the reaction zone portion for extracting atleast one reaction waste product from the second enclosed chamber.

In one or more embodiments, the wall defining the second enclosedchamber of the reaction zone portion comprises at least one materialthat is substantially gas-impermeable and resistant to a temperature ofat least 200° C.

In one or more embodiments, the at least one material that issubstantially gas-impermeable and resistant to a temperature of at least200° C. is selected from the group consisting of quartz and stainlesssteel.

In one or more embodiments, the first inlet for introducing carrier,support, and/or reactant gases and at least one liquid reactant solutioninto the first enclosed chamber of the preheating zone portion isoperatively connected to a pump that is connected to a liquid reactantsolution container or mixer.

In one or more embodiments, the vertical distance between the top andthe bottom of the preheating zone portion and the ultrasonic atomizingnozzle are configured to enable droplets of the at least one liquidreactant solution sprayed from the ultrasonic atomizing nozzle to have asubstantially uniform velocity prior to entering the reaction zoneportion.

In one or more embodiments, the vertical chemical vapor depositionreactor further comprises a product collector connected to the bottom ofthe reaction zone portion.

In one or more embodiments, the top of the preheating zone portionfurther comprises a second inlet through which an evacuation gas can beintroduced into the first enclosed chamber to displace and remove the atleast one reaction waste product.

In one or more embodiments, the vertical chemical vapor depositionreactor includes a preheating zone portion comprising a first enclosedchamber and having a top, a bottom, and sides with a wall defining thefirst enclosed chamber; a first inlet located at the top of thepreheating zone portion for introducing carrier, support, and/orreactant gases and at least one liquid reactant solution into the firstenclosed chamber; an ultrasonic atomizing nozzle operatively connectedto the first inlet for releasing the carrier, support, and/or reactantgases and the at least one liquid reactant solution inside the firstenclosed chamber; a reaction zone portion comprising a second enclosedchamber and having a top connected to and in fluid communication withthe bottom of the preheating zone portion, a bottom, and sides with awall defining the second enclosed chamber; a heater interposed betweenthe top and the bottom of the reaction zone portion for heating thecarrier, support, and/or reactant gases and the at least one liquidreactant solution; a cooling zone portion comprising a third enclosedchamber and having a top connected to and in fluid communication withthe bottom of the reaction zone portion, a bottom, and sides with a walldefining the third enclosed chamber, and an outlet at the bottom of thecooling zone portion for extracting at least one reaction waste productfrom the third enclosed chamber.

In one or more embodiments, the bottom of the cooling zone portion isconnected to a product collector.

In one or more embodiments, the first inlet for introducing carrier,support, and/or reactant gases and at least one liquid reactant solutioninto the first enclosed chamber of the preheating zone portion isoperatively connected to a pump that is connected to a liquid reactantsolution container or mixer.

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 illustrates, in correspondence with one embodiment of the presentdisclosure, an exemplary vertical chemical vapor deposition reactor 100,preferably used for synthesizing metal oxide impregnated carbonnanotubes.

FIG. 2 is a graphical presentation showing the velocity profile ofliquid reactant solution droplets sprayed from the tip of a wide rangeultrasonic atomizing nozzle installed on the top of the preheating zoneof a chemical vapor deposition reactor according to Example 1.

FIG. 3 illustrates, in correspondence with another embodiment of thepresent disclosure, another exemplary vertical chemical vapor depositionreactor 300, preferably used for synthesizing metal oxide impregnatedcarbon nanotubes.

FIG. 4 illustrates a vertical chemical vapor deposition reactor used tosynthesize aluminum oxide impregnated multi-walled carbon nanotubesaccording to Example 1.

FIG. 5 is an SEM image of the pure multi-walled carbon nanotubesaccording to Example 2.

FIG. 6 is an SEM image of the aluminum oxide impregnated multi-walledcarbon nanotubes according to Example 2.

FIG. 7 is a TEM image of the pure multi-walled carbon nanotubesaccording to Example 2.

FIG. 8 is a TEM image of the aluminum oxide impregnated nanotubesaccording to Example 2.

FIG. 9A is a graphical presentation showing the area of the aluminumoxide impregnated multi-walled carbon nanotube sample selected for theEDS analysis according to Example 2.

FIG. 9B is a graphical presentation of the EDS spectrum from the EDSanalysis of the selected area of the aluminum oxide impregnatedmulti-walled carbon nanotube sample shown in FIG. 9A according toExample 2.

FIG. 10 is a graphical presentation of the XRD analysis result of thealuminum oxide impregnated multi-walk-d carbon nanotubes according toExample 2.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Various embodiments are described hereinafter with reference to thefigures. It should be noted that the figures are not drawn to scale andthat elements of similar structures or functions are represented by likereference numerals throughout the figures. It should also be noted thatthe figures are only intended to facilitate the description of theembodiments. They are not intended as an exhaustive description of theinvention or as a limitation on the scope of the invention. In addition,an illustrated embodiment needs not have all the aspects or advantagesshown. An aspect or an advantage described in conjunction with aparticular embodiment is not necessarily limited to that embodiment andcan be practiced in any other embodiments even if not so illustrated.

A first aspect of the disclosure relates to a chemical vapor deposition(CVD) reactor equipped with an ultrasonic atomizing nozzle toadvantageously use both gases and liquid reactant solutions as startingmaterials to carry out a chemical vapor deposition reaction. Referringto FIG. 1, one embodiment of the CVD reactor designated 100 is avertical CVD reactor that includes a preheating zone portion 110 and areaction zone portion 140.

The preheating zone portion 110 includes a first enclosed chamber 113defined by the first enclosed chamber (inside) wall 114 that surroundsthe first enclosed chamber 112 on the sides. The preheating zone portion110 has a top 116, which may be a removable top plate and which has afirst inlet 118 for introducing gases, such as a earner gas (e.g. He,N₂, and Ar), a support gas (e.g. CO₂, H₂O, H₂, and NH₃), and/or areactant gas (e.g. a carbon-containing gas to synthesize carbonnanotubes, such as methane, ethane, propane, and carbon monoxide), andone or more liquid reactant solutions for a CVD reaction into the firstenclosed chamber 112. The first inlet 118 is operatively connected to anultrasonic atomizing nozzle 120, a type of spray nozzle, with the tip122 of the ultrasonic atomizing nozzle 120 located inside the firstenclosed chamber 112 for releasing the gases and the liquid reactantsolution(s) inside the first enclosed chamber 112. The bottom 124 of thepreheating zone portion 110 is connected to and in fluid communicationwith a top 146 of the reaction zone portion 140, i.e. the gases and theliquid reactant solution(s) entering into the first enclosed chamber 112can enter into the reaction zone portion 140 via the top 146 of thereaction zone portion 140.

The ultrasonic atomizing nozzle 120 converts electrical energy intomechanical energy in the form of ultrasonic vibrations that atomize aliquid into tiny droplets with sizes in the micron range. The ultrasonicatomizing nozzle operates at a specific resonant frequency, which isdetermined primarily by the length of the nozzle, the size of thedroplets is governed by the resonant frequency of the ultrasonicatomizing nozzle (i.e. the higher the resonant frequency, the smallerthe median droplet size) and by the surface tension and the density ofthe liquid being atomized. In some embodiments, the ultrasonic atomizingnozzle 120 has a resonant frequency of 10-200 kHz, 15-180 kHz, 20-150kHz, 20-120 kHz, 20-100 kHz, 40-80 kHz, or 50-70 kHz, to produce liquiddroplets with a median droplet size of about 10-140 microns, about30-120 microns, about 50-100 microns, or about 70-90 microns. The mediandroplet size defines the 50% point in droplet size—that is, one-half ofthe number of droplets in the spray have diameters larger that thisvalue while the other half have diameters smaller than this value.

The ultrasonic atomizing nozzle 120 in the preheating zone portion 110generates a soft, non-pressurized, low velocity spray of the liquidreactant solution(s), typically on the order of 3-5 inches per second,advantageously reducing the amount of overspray and leading tosubstantial material savings and a reduction in the waste dischargedinto the environment, since the droplets of the spray tend to settle ona surface they come into contact with, for example, the inside wall 144of the reaction zone portion 140, to form the CVD reaction productsrather than bounce off the surface. Additionally, by controlling theflow rates of the gases that also travel through the ultrasonicatomizing nozzle 120 via the first inlet 118 and by equipping theultrasonic atomizing nozzle 120 with a specialized type of spray shaperattached to the tip 122, the spray pattern may be controlled and shaped,for example, from as small as 0.070 inches wide to as much as 1-2 feetwide. FIG. 2 illustrates an ultrasonic atomizing nozzle with a widerange tip according to the Examples of the present disclosure thatproduced a liquid droplet spray almost as wide as the diameter of thetube-shaped first enclosed chamber of the preheating zone portion of theCVD reactor, with the ultrasonic atomizing nozzle positioned at thecenter on the top plate of the preheating zone portion. The wide rangetip of the ultrasonic atomizing nozzle is capable of dispersing dropletsover a wide area because of an angled portion of the tip. As liquidrides up the tip, droplets are pulverized on an angle and pushed awayfrom the nozzle. To further increase the spray area covered by thenozzle, the wide range tip can be attached to an appropriate sprayshaper. e.g. a Dove Tail Spray Shaper manufactured by Sonaer Ultrasonics(Farmingdale, N.Y., USA), such that as the ultrasonic atomizing nozzlesprays the liquid, the air from the spray shaper will spread thedroplets over a greater area, for example, with a spray angle of fromabout 20 degrees to 34 degrees and a spray diameter of 2-3 inches whenthe Dove Tail Spray Shaper is used. Preferably, the width of the liquiddroplet spray, the initial velocity of the liquid droplets exiting thetip of the ultrasonic atomizing nozzle that has both a radial and avertical velocity component, and the height of the preheating zoneportion, i.e. the vertical distance between the top and the bottom ofthe preheating zone portion, are properly controlled and adjusted suchthat (substantially) all of the liquid droplets have a substantiallyuniform downward velocity prior to entering the reaction zone portion asshown in FIG. 2 to supply (substantially) all of the input liquidreactant solution to the reaction zone portion (without a loss of theinput liquid reactant solution due to an undesirable contacting of theliquid reactant solution droplets with the inside wall of the firstenclosed chamber of the preheating zone portion), and form a desiredreaction product with homogeneous physical and chemical characteristics.In a preferred embodiment, the first enclosed chamber 112 of thepreheating zone portion 110 is tube-shaped or cylindrically shaped. Insome embodiments, the ultrasonic atomizing nozzle 120 has a wide rangetip capable of generating a spray with a width that is at least 70%,preferably at least 80%, more preferably at least 90%, or mostpreferably at least 95% of the width or diameter of the first enclosedchamber 112 of the preheating zone portion 110.

The preheating zone portion 110 preferably further comprises apreheating element 126 to ensure the attainment of the desiredtemperature for the liquid reactant solution(s) and the gas flow in thereaction zone portion 140. The preheating element 126, which may be agas heater or furnace, or an electrical heater or furnace, may beinstalled within the first enclosed chamber 112, or surrounding theoutside wall 130 of the first enclosed chamber 112, or at the tubing ofthe first inlet 118 on the top 116 of the preheating zone portion 110.The preheating element 126 preferably operates at a lower temperaturee.g. 100 to 1200° C., than the chosen CVD reaction temperature, e.g.200-1400° C.

The reaction zone portion 140 has a second enclosed chamber 142 definedby the second enclosed chamber inside wall 144 surrounding the secondenclosed chamber 142. In a preferred embodiment, the second enclosedchamber 142 of the reaction zone portion 140 is tube-shaped orcylindrically shaped, the bottom 154 of the reaction zone portion 140,which may be a removable bottom plate, has an outlet 158 for extractingthe input carrier, support, and reactant gases and vaporized liquidreactant solution(s), and/or reaction waste products from the secondenclosed chamber 142. The outlet 158 may be connected to a vacuum pump(not shown) to facilitate the extraction and removal of the input andwaste product gases. To provide a high reaction temperature, such as200-1400° C., 400-1200° C., 500-1000° C., 600-900° C., 750-900° C., or850° C., in the second enclosed chamber 142 of the reaction zone portion140, a heater 156, such as a gas heater or furnace and an electricheater or furnace, is installed between the top 146 and the bottom 154of the reaction zone portion 140 for heating the input (carrier,support, and/or reactant) gases and the liquid reactant solutiondroplets to a desired temperature to generate active species for the CVDreaction. For example, a furnace may be installed adjacent, orpreferably surrounding, the outside wall 160 of the second enclosedchamber 142 of the reaction zone portion 140 to provide heat, preferablysubstantially evenly distributed heat, to the second enclosed chamber142 to reach a desired CVD reaction temperature within a range describedabove. Alternatively, one, or preferably a plurality of electricallypowered heat generating filament networks may be installed, eithervertically (i.e. in parallel to the gas and liquid reactant solutiondroplet flows) or horizontally (i.e. perpendicular to the gas and liquidreactant solution droplet flows) between the top 146 and the bottom 154of the reaction zone portion 140 to preferably provide substantiallyevenly distributed heat within the second enclosed chamber 142. Thefilament network may be made of 0.1-3 mm, 0.2-1.5 mm, or 0.5-1 mmdiameter resistively beatable metal wires that may be parallel and/ortwisted to provide a large heating area. Suitable material for the metalwires of the filament network include, without limitation, tantalum,tungsten, molybdenum, rhenium, and mixtures thereof. In someembodiments, the filament network comprises a composite material havinga core of material selected from the group consisting of a ceramic,graphite, carbon fiber, and carbon-carbon composite and an outer coatingof a material selected from the group consisting of tantalum, tungsten,molybdenum, rhenium, and mixtures thereof. A thicker wire is preferablyused in the filament network to provide a stronger structural integrityand longer use life.

The material for the inside wall 114 of the first enclosed chamber 112of the preheating zone portion 110 is preferably strong, substantiallyresistant to corrosion, substantially gas-impermeable, and inert to theinput gases and the liquid reactant solution(s)) for a CVD reaction. Thematerial for the inside wall 144 of the second enclosed chamber 142 ofthe reaction zone portion 140 is preferably substantiallygas-impermeable, inert to the input gases and the liquid reactantsolution(s) for a CVD reaction, and resistant to a high temperature,such as 200-1400° C., 400-1200° C., 500-1000° C., 600-900° C., and750-900° C., or 850° C. Non-limiting examples of the suitable materialfor the walls of the first enclosed chamber and the second enclosedchamber include quartz and metal, such as stainless steel.

Insulation 162 is preferably provided around the preheating zone portion110 and the reaction zone portion 140 to control the temperature andensure a sale and economic operation of the CVD reactor. The insulationmay be provided by a graphite foam or quartz wool.

In a preferred embodiment, the first inlet 118 on the top 116 of thepreheating zone portion 110 for introducing the input gases and theliquid reactant solution(s)) into the first enclosed chamber 112 of thepreheating zone portion 110 is operatively connected to a pump 164 thatis connected to a liquid reactant solution container or mixer 166 shownin FIG. 1. In some embodiments, the pump 164 is a gear pump, aninjection or syringe pump, or a peristaltic pump. A valve 168 ispreferably installed on the connective line between the liquid reactantsolution container/mixer 166 and the pump 164 to help control the flowrate of the liquid reactant solution fed to the ultrasonic atomizingnozzle 120 via the first inlet 118 on the top 116 of the preheating zoneportion 110. Since the ultrasonic atomization process does not rely onpressure, the amount of the liquid reactant solution atomized per unittime is primarily determined by the flow rate of the liquid reactantsolution controlled by the pump 164 and/or the valve 168. The flow rateof the liquid reactant solution suitable for the ultrasonic atomizationmay vary widely, depending on the type of the ultrasonic atomizingnozzle used, particularly the size of its orifice through which theliquid reactant solution emerges onto the atomizing surface of thenozzle, the atomizing surface area, and the operating frequency, theviscosity of the liquid reactant solution, and the presence of any verylong-chained polymer molecules and/or undissolved solids in the liquidreactant solution. In some embodiments, the flow rate of the liquidreactant solution is in the range of 1 ml/h to 16 L/h, 10 ml/h to 10L/h, 50 ml/h to 5 L/h, 100 ml/h to 1 L/h, 200-800 ml/h, or 400-600 ml/h.

Likewise, a valve 170 may be preferably installed on the connective linebetween the input gas sources and the first inlet 118 on the top 116 ofthe preheating zone portion 110 to control, the flow rates of the inputgases also fed to the ultrasonic atomizing nozzle 120 via the firstinlet 118.

Since the bottom 154 of the reaction zone 140 and the top 116 of thepreheating zone portion 110 isolate the reactor, the interior of thereactor, i.e. the first enclosed chamber 112 and the second enclosedchamber 142, can be evacuated without significant inward leakage fromthe surrounding ambient atmosphere. In another preferred embodiment, thetop 116 of the preheating zone portion 110 further comprises a secondinlet 119 through which an evacuation gas can be introduced into thefirst enclosed chamber 112. With the evacuation gas further flowing intothe second enclosed chamber 142 of the reaction zone portion 140 andexiting the CVD reactor 100 through the outlet 158 at the bottom 154 ofthe reaction zone portion 140, the evacuation gas displaces and removesexcess input gases and vaporized liquid reactant solution(s), andgaseous reaction waste products from the CVD reactor 100. Non-limitingexamples of the suitable evacuation gas include air and inert gases,such as argon, helium, and nitrogen.

Since in some embodiments a desired CVD reaction product, e.g. carbonnanotubes, deposits on the inside wall 144 of the second enclosedchamber 142 of the reaction zone portion 140, a product collector (notshown in FIG. 1) may be (detachably) connected to the bottom 154 of thereaction zone portion 140 to collect the CVD reaction product that hasbeen separated from the inside wall 144 of the second enclosed chamber142 by scraping or brushing, for example.

After a CVD reaction taking place in the second enclosed chamber 142 ofthe reaction zone portion 140 is complete, to lower the temperature ofthe second enclosed chamber 142 quickly so that the CVD reaction productcan be expeditiously collected from the inside wall 144 of the secondenclosed chamber 142, in a preferred embodiment shown in FIG. 3, the CVDreactor 300 further comprises a cooling zone portion 180 in addition tothe preheating zone portion 110 and the reaction zone portion 140. Inthis embodiment, the cooling zone portion 180 comprises a third enclosedchamber 182 and has a top 186 connected to and in fluid communicationwith the bottom 154 of the reaction zone portion 140, a bottom 194, andsides with a wall, i.e. inside wall 184, defining the third enclosedchamber 182. The third enclosed chamber 182 of the cooling zone portion180 is preferably tube-shaped or cylindrically shaped. Like the insidewall 114 of the first enclosed chamber 112 and the inside wait 144 ofthe second enclosed chamber 142, the inside wall 184 of the thirdenclosed chamber 182 is preferably made of a material that issubstantially gas-impermeable and resistant to a high temperature, suchas quartz and stainless steel. With the addition of the cooling zoneportion 180, the outlet 198 of the CVD reactor 300 preferably positionedon the bottom 194 of the cooling zone portion 180 instead of the bottom154 of the reaction zone portion 140 to extract any excess input gasesand vaporized liquid reactant solution(s) and gaseous CVD reaction wasteproducts from the CVD reactor 300, optionally with the help of anevacuation gas supplied to the CVD reactor 300 via the second inlet 119on the top of the preheating zone portion 110 as described above. Thecooling effect provided by the cooling zone portion 180 may be achievedby, for example, circulating cool air or water, or a cool refrigerant ina network of tubing attached to the outside wall 200 and/or inside wall184 of the third enclosed chamber 182, by pumping cool air into thethird enclosed chamber 182, or by placing the cooling zone portion 180in a low temperature environment, such as a refrigerator and a coolwater or ice/water bath. A product collector (not shown in FIG. 3) maybe (detachably) attached to the bottom 194 of the cooling zone portion180 to collect the CVD reaction product separated from the inside wall144 of the second enclosed chamber 142 of the reaction zone portion 140.In this preferred embodiment, the first inlet 118 for introducing theinput (carrier, support, and/or reactant) gases and the liquid reactantsolution(s)) into the first enclosed chamber 112 of the preheating zoneportion 110 may be operatively connected to the pump 164 that isconnected to the liquid reactant solution container or mixer 166, andthe ultrasonic atomizing nozzle 120 and the height of the preheatingzone portion 110 are configured to enable droplets of the liquidreactant solution(s)) sprayed from the ultrasonic atomizing nozzle 120to have a substantially uniform velocity prior to entering the reactionzone portion 110 as described above.

In another embodiment, the disclosed CVD reactor may be horizontal, i.e.the preheating zone portion, the reaction zone portion, and the cowlingzone portion if included, are horizontally positioned and horizontallyconnected to each other.

A second aspect of the disclosure relates to a method of synthesizingcarbon nanotubes impregnated with at least one metal oxide, preferablyby using the chemical vapor deposition reactor described in the firstaspect of the present disclosure. The method includes (a) subjecting aliquid reactant solution to atomization in the presence of at least onegas flow comprising at least one carrier gas and at least one supportgas, wherein the liquid reactant solution comprises at least one organicsolvent, at least one metallocene, and at least one metal alkoxide, toform an atomized mixture comprising droplets of the liquid reactantsolution and the at least one gas flow, and (b) heating the atomizedmixture to a temperature of 200° C.-1400° C., wherein the heating formsat least one metal oxide and at least one carbon source compound,wherein the at least one metallocene catalyzes the formation of carbonnanotubes from the at least one carbon source compound and the at leastone metal oxide is incorporated into or on a surface of the carbonnanotubes to form the carbon nanotubes impregnated with the at least onemetal oxide.

In one embodiment, the disclosed method results in the synthesis ofsingle-walled carbon nanotubes impregnated with at least one metaloxide.

In another embodiment, the disclosed method results in the synthesis ofmulti-walled carbon nanotubes impregnated with at least one metal oxide.In some embodiments, the multi-walled carbon nanotubes may have astructure conforming to the Russian Doll model, i.e. they contain sheetsof graphite arranged in concentric cylinders. In other embodiments, themulti-walled carbon nanotubes have a structure conforming to theParchment model, i.e. they contain a single sheet of graphite rolled inaround themselves and resemble a scroll of parchment.

The liquid reactant solution may be atomized to form a line spray in avariety of ways, including, but not limited to, electrostaticsprocesses, centrifugal forces, and preferably ultrasonic atomization.Ultrasonic atomization occurs when a liquid film is placed on a smoothsurface that is set into vibrating motion such that the direction ofvibration is perpendicular to the surface. The liquid absorbs some ofthe vibrational energy, which is transformed into standing waves. Thesewaves, known as capillary waves, form a rectangular grid pattern in theliquid on the surface with regularly alternating crests and troughsextending in both directions. When the amplitude of the underlyingvibration is increased, the amplitude of the waves increasescorrespondingly; that is, the crests become taller and troughs deeper. Acritical amplitude is ultimately readied at which the height of thecapillary waves exceeds that required to maintain their stability. Theresult is that the waves collapse and tiny droplets of liquid areejected from the tops of the degenerating waves normal to the atomizingsurface.

In one embodiment the ultrasonic atomization of the liquid reactantsolution is achieved by feeding the liquid reactant solution to anultrasonic atomizing nozzle that uses high frequency sound wavesproduced piezoelectric transducers acting upon the nozzle tip that willcreate capillary waves in a liquid film. Once the amplitude of thecapillary waves reach a critical height (due to the power level suppliedby the generator of the ultrasonic atomizing nozzle), they become tootall to support themselves and tiny droplets fall off the tip of eachwove resulting in atomization. The size of the droplets is primarilydetermined by the frequency of vibration (i.e. the higher the frequency,the smaller the droplet size), and the surface tension and viscosity ofthe liquid reactant solution. In some embodiments, the frequency ofvibration for the ultrasonic atomization of the liquid reactant solutionis 10-200 kHz, 15-180 kHz, 20-150 kHz, 20-120 kHz, 20-100 kHz, 40-80kHz, or 50-70 kHz. In some embodiments, the median droplet size ordiameter of the liquid reactant solution that has been subjected to theultrasonic atomization is about 10-140 microns, about 30-120 microns,about 50-100 microns, or about 70-90 microns. Subjecting the liquidreactant solution to atomization, preferably ultrasonic atomization, orpreferably in the chemical vapor deposition reactor described in thefirst aspect of the present disclosure, advantageously results in theformation of small and uniform liquid reactant solution droplets thatpromotes the formation of the metal oxide impregnated carbon nanotubeswith substantially uniform physical and chemical characteristics, suchas the length and diameter of the carbon nanotubes, the weightpercentage of the metal oxide relative to the total weight of the metaloxide impregnated carbon nanotubes, and the distribution of the metaloxide particles on the surface of the carbon nanotubes.

An ultrasonic atomizing nozzle ordinarily delivers a soft, low-velocity,and narrow spray. The disclosed method advantageously includes thepresence of at least one gas flow comprising at least one carrier gasand at least one support gas during the (ultrasonic) atomization of theliquid reactant solution to shear the spray to a desired width andpropel the spray in a desired direction, for example, in a uniformwedge-shaped pattern shown in FIG. 2, producing a wide uniform spraypattern. In some embodiments, the flow rate of the at least one carriergas may be 500-2000 sccm, 700-1800 sccm, preferably 900-1600 sccm, ormore preferably 1000-100 sccm, and the flow rate of the at least onesupport gas may be 1500-6000 sccm, 2000-5500 sccm, 2500-5000 sccm, orpreferably 3000-4500 sccm. In some embodiments, the combined gas flowrate is between 1 mL/min and 10 L/min, between 10 mL/min and 5 L/min,between 50 mL/min and 1 L/min, between 100 mL/min and 750 m L/min,between 150 mL/min and 500 mL/min, or between 200 mL/min and 250 mL/min.In some embodiments, the uniform spray pattern resulting from theultrasonic atomization of the liquid reactant solution in the presenceof the at least one gas flow may be 2-20 inches wide, or 5-18 incheswide, or 8-16 inches wide.

In some embodiments, the at least one carrier gas is preferably an inertgas selected from the group consisting of He, N₂, and Ar.

In some embodiments, the at least one support gas comprises a gas thatis slightly oxidative to remove amorphous carbon, such as CO₂ and H₂O,and/or preferably a reducing gas such as H₂ and NH₃.

The liquid reactant solution comprises at least one organic solvent,non-limiting examples of which include 2-methoxy ethanol, 2-ethoxyethanol, 2-methoxy propanol, 2-ethoxy propanol, 2-propoxy propanol,2-butoxy propanol, 2-butoxy butanol, and liquid hydrocarbons, such ascyclohexane, heptane, octane, benzene, toluene, ethyl benzene, xylene,cumene, and styrene. In the disclosed method, the organic solvent canalso act as a carbon source compound and/or produce one or more carbonsource compounds for the formation of carbon nanotubes during theheating.

Additionally, the liquid reactant solution comprises at least one metalalkoxide. Depending on the metal oxide(s) desired to be incorporatedinto or on the surface of the carbon nanotubes, non-limiting examples ofsuitable metal alkoxides include an aluminum alkoxide, a titaniumalkoxide, a magnesium alkoxide, a calcium alkoxide, a strontiumalkoxide, a barium alkoxide, a scandium alkoxide, a yttrium alkoxide, azirconium alkoxide, a lanthanum alkoxide, a vanadium alkoxide, and asilicon alkoxide. Preferred metal alkoxides include metal ethoxides,metal propoxides, metal isopropoxides, metal butoxides, metalisobutoxides, and metal tert-butoxides. In a preferred embodiment, theat least one metal alkoxide is one or more metal alkoxy alkoxides thatare generally highly soluble in an organic solvent, e.g. having asolubility of at least 15 weight percent, at ambient temperature(approximately 20° C.) in toluene, or 2-methoxy ethanol, or 2-butoxybutanol. Non-limiting examples of preferred metal alkoxy alkoxidesinclude (Z—(CH₂)_(n)—O)—Mg—(O—(CH₂)_(m)—OR₂),(Z—(CH₂)_(n)—O)—Ca—(O—(CH₂)_(m)—OR₂),(Z—(CH₂)_(n)—O)-M2-(O—(CH₂)_(m)—OR₂), and

wherein M2 is a Group IIA metal selected from strontium or barium; M3 isa Group IIIA metal selected from scandium, yttrium or lanthanum; m, nand p are the same or different positive integers from 1 to 12; Z is(R₁O)— or (R₁)—, and R₁ and R₂ are the same or different hydrocarbylradicals of from 1 to 20 carbon atoms. Particularly preferred R₁ groupsare those with one to tour carbon atoms, such as methyl, ethyl, propyl,and butyl.

In some embodiments, more than one metal alkoxide is included in theliquid reactant solution to synthesize carbon nanotubes impregnated withmore than one metal oxide produced from the more than one metalalkoxide.

Metallocenes are a type of sandwich compound, an organometallic complexfeaturing a metal bound by haptic covalent bonds to two arene ligands. Ametallocene is a compound typically consisting of two substituted orunsubstituted cyclopentadienyl anions (Cp, which is C₅H₅) bound to ametal center (M) in the oxidation state II or IV, with the resultinggeneral formula (C₅H₅)₂M or (C₅H₅)₂MX₂, e.g., titanocene dichloride,vanadocene dichloride. There are other metallocenes that have bent ortilted Cp rings with additional ligands (L) with the general formula of(η-C₃H₅)₂ML, and that have only one Cp ligand with additional ligands(L) with the general formula of (η-C₃H₅)₂ML. The liquid reactantsolution further comprises at least one metallocene, preferably ametallocene of Ni, a metallocene of Co, a metallocene of Fe, ametallocene of Cr, a metallocene of Mo, a metallocene of Rh, ametallocene of Ti, a metallocene of W, a metallocene of V, and ametallocene of Zr.

When heated to a temperature of 200-1400° C., 400-1200° C., preferably500-1000° C., preferably 600-900° C., more preferably 750-900° C., ormore preferably 850° C., according to the disclosed method, the metalalkoxide in the liquid reactant solution droplets of the atomizedmixture forms a metal oxide and/or one or more carbon source compounds,e.g. an alkene, for the formation of carbon, nanotubes (e.g. the carbonsource compound is further catalytically cracked on the surface of ametal particle catalyst produced from the metallocene described below togenerate carbon atoms), and the metallocene in the liquid reactantsolution droplets of the atomized mixture forms metal particles,preferably the metal particles of Ni, Co, Fe, Cr, Mo, Rh, Ti, W, V, andZr, that catalyze the formation of carbon nanotubes (e.g. following thecontacting of the carbon source compound (gas) with the metal particlecatalyst, the carbon generated from the cracking of the carbon sourcecompound is dissolved into the metal particles, and after oversaturationof the carbon in the metal particles, continuous growth of the carbonnanotubes from the metal particles takes place in the presence of astable carbon source compound (gas) supply to the metal particles), andstill additional one or more carbon source compounds (e.g. CH₄ and C₅H₆)for the formation of single-walled or multi-walled carbon nanotubes, asdisclosed by Clarence S. Yah. Geoffrey S. Simate, Kapil Moothi, Kwena S.Maphutha, and Sunny E. Iyuke, Synthesis of Large Carbon Nanotubes fromFerrocene: The Chemical Vapour Deposition Technique, Trends in AppliedSciences Research 6 (11): 1270-1279, 2011; Amelia Barreiro, SilkeHampel, Mark H. Rümmeli, Christian Kramberger, Alexander Grüneis, KatiBiedermann, Albrecht Leonhardt, Thomas Gemming, Bernd Büchner, AdrianBachtold, and Thomas Pichler, Thermal Decomposition of Ferrocene as aMethod for Production of Single-Walled Carbon Nanotubes withoutAdditional Carbon Sources, J. Phys. Chem. B, 2006, 110 (42), pp20973-20077; each incorporated herein by reference in their entirety.

In some embodiments, the heating is performed at a heating rate of0.01-50° C./min, 0.05-45° C./min, 0.1-40° C./min, 0.5-30° C./min, 1-20°C./min, or 5-10° C./min. In some embodiments, the duration of theheating is 1-1200 min, 5-1000 min, 10-900 min, 30-800 mm, 50-700 min,100-600 trim, 150-500 min, or 200-400 min. With the heating of theliquid reactant solution droplets taking place in the presence of thegas flow of the carrier gas and the support gas, the vaporized liquidreactant solution droplets are mixed with the gas flow to form the metaloxide impregnated carbon nanotubes. When the disclosed method isimplemented in a chemical vapor deposition reactor, preferably in thechemical vapor deposition reactor according to the first aspect of thepresent disclosure, the gas flow advantageously maximize the dispersionof the vaporized organic solvent(s), metallocene(s) and metalalkoxide(s), and their reaction products throughout the reaction zone ofthe chemical vapor deposition reactor, thus effectively utilizing thefull capacity of the chemical vapor deposition reactor to maximize thesynthesis of the metal oxide impregnated carbon nanotubes, facilitatingan efficient contact of the gaseous carbon source compounds (e.g.alkenes, CH₄, and C₅H₆) with the catalyst (i.e. the metal particles),reducing agglomeration of the carbon nanotubes and/or the metal oxideparticles incorporated into or on the surface of the carbon nanotubes,and promoting homogeneous physical and chemical characteristics of themetal oxide impregnated carbon nanotubes.

The concentration of the at least one metal alkoxide in the liquidreactant solution may be 0.1-50%, 0.5-45%, 1-40%, 5-35%, 10-30%, or15-20% of the total weight of the liquid reactant solution. Theconcentration of the at least one metallocene in the liquid reactantsolution may be 0.1-50%, 0.5-45%, 1-40%, 5-35%, 10-30%, or 15-20% of thetotal weight of the liquid reactant solution. The weight ratio of the atleast one metal alkoxide to the at least one metallocene in the liquidreactant solution may be from 10:1 to 1:10, from 8:1 to 1:8, from 5:1 to1:5, from 3:1 to 1:3, from 2:1 to 1:2, or 1:1. By varying the totalamount of the liquid reactant solution, the concentrations of the metalalkoxide(s) and the metallocene(s) in the liquid reactant solution, andthe weight ratio of the metal alkoxide(s) to the metallocene(s), thereaction temperature, pressure, and time, the amount of the support gas,e.g. hydrogen gas, that prevents or limits deactivation of the catalyst,etc, in some embodiments, the carbon nanotubes synthesized by thedisclosed method comprise the metal particle catalyst encapsulatedinside the carbon nanotubes, have a length of 50 nm-100 μm, 75 nm-50 μm,100 nm-25 μm, 150 nm-10 μm, 200 nm-5 μm, 300 nm-1 μm, 400 nm-900 nm, 500nm-800 nm, 600 nm-700 nm, or greater than 0.1 mm, greater than 0.5 mm,greater than 1 mm, greater than 5 mm, or greater than 1 cm; have anaverage outer diameter of about 1-100 nm, about 5-90 nm, about 10-70 nm,about 20-50 nm, about 30-40 nm; and have about 5-90%, about 10-80%,about 20-60%, about 30-50% of their surfaces covered by the metal oxideparticles.

In one embodiment, the metal oxide particles form a layer covering anexterior surface and/or an interior surface of the carbon nanotubes. Inanother embodiment, the metal oxide particles are sandwiched betweensurfaces of the carbon nanotubes.

In another embodiment, the metal oxide particles are incorporated intothe carbon nanotubes. For example, the metal oxide particles are mixedwith and/or integrated into the carbon nanotubes, and/or embedded withinor among graphite sheets of the carbon nanotubes, and/or completely orpartially embedded within a surface of the carbon nanotubes.

In some embodiments, the average particle size or diameter of the metaloxide particles incorporated into or on the surface of the carbonnanotubes may be about 1-200 nm, about 1-180 nm, about 5-150 nm, about5-100 nm, about 10-80 nm, about 15-60 nm, or about 20-40 nm.

In one embodiment, the metal oxide particles are aluminum oxideparticles which are produced from an aluminum alkoxide (e.g. aluminumisopropoxide) and which may have various crystalline phases. In oneembodiment, the aluminum oxide particles comprise α—Al₂O₃ (i.e. aluminumoxide in corundum crystalline phase). In another embodiment, thealuminum oxide particles comprise γ-Al₂O₃. In another embodiment, thealuminum oxide particles comprise η-Al₂O₃. In another embodiment, thealuminum oxide particles comprise θ-Al₂O₃. In another embodiment, thealuminum oxide particles comprise χ-Al₂O₃. In another embodiment, thealuminum oxide particles comprise κ-Al₂O₃. In still another embodiment,the aluminum oxide particles comprise δ-Al₂O₃.

In some embodiments, to supply still more carbon source compounds forthe formation of carbon nanotubes, the at least one gas flow and/or theliquid reactant solution may further comprise one or more additionalcarbon-containing compounds selected from, without limitation, ethylene,pentene, cyclopentadiene, methane, ethane, propane, butane, butadiene,pentane, hexane, cyclohexane, carbon monoxide, carbon dioxide, benzene,xylene, and toluene.

The disclosed method may be carried out under an atmospheric pressure, alow-pressure, or a vacuum. If the method is carried out under anatmospheric pressure, helium may be preferably used as a carrier gas, sothat it is possible to minimize damage to the carbon nanotubes caused bycollisions against heavy argon (Ar) at high temperatures. If the methodis carried out under a low pressure or a vacuum, hydrogen (H₂) may bepreferably used as a support gas to deoxidize an oxidized surface of themetal particle catalyst at a high temperature, so that high-qualitycarbon nanotubes can be formed.

In one embodiment, the at least one metal alkoxide in the liquidreactant solution is aluminum isopropoxide, which forms aluminum oxidewhen the atomized mixture comprising the droplets of the liquid reactantsolution and the at least one gas flow is heated. In some embodiments,the resulting product is multi-walled carbon nanotubes impregnated withaluminum oxide which have a BET surface area of 450-2000 m²/g, 600-1900m²/g, 700-1800 m²/g, 800-1700 m²/g, 900-1600 m²/g, 1000-1500 m²/g, or1100-1300 m²/g. In some embodiments, the resulting product issingle-walled or multi-walled carbon nanotubes impregnated with aluminumoxide that comprise Al in an amount of 5-20%, 5-15%, or 10-15% of thetotal weight of the single-walled or multi-walled carbon nanotubesimpregnated with the aluminum oxide. In some embodiments, the resultingproduct is single-walled or multi-walled carbon nanotubes impregnatedwith aluminum oxide, with 1-99 wt %, 5-90 wt %, 10-80 wt %, 20-70 wt %,30-60 wt %, or 40-50 wt % of the aluminum oxide particles incorporatedinto or on the surface of the carbon nanotubes being in corundum phase.

In one embodiment, the method further comprises collecting the carbonnanotubes impregnated with the at least one metal oxide. For example,when the disclosed method is implemented with a CVD reactor, such as theone described in the first aspect of the disclosure, the metal oxideimpregnated carbon nanotubes may be attached to the wall of the reactionzone of the CVD reactor. In order to collect them, the metal oxideimpregnated carbon nanotubes have to be separated from the wall byscraping, brushing, or other means.

Although particular embodiments have been shown and described, it willbe understood that they are not intended to limit the presentinventions, and it will be obvious to those skilled in the art thatvarious changes and modifications may be made without departing frontthe spirit and scope of the present inventions. The specification anddrawings are, accordingly, to be regarded in an illustrative rather thanrestrictive sense. The present disclosure is intended to coveralternatives, modifications, and equivalents, which may be includedwithin the spirit and scope of the present inventions as defined by theclaims.

Having generally described this invention, a further understanding canbe obtained by reference to certain specific examples which are providedherein for purposes of illustration only and are not intended to belimiting unless otherwise specified.

Example 1 Materials and Methods

1. Materials

p-Xylene (C₈H₁₀, 96-99%), ferrocene ((C₅H₅)₂Fe, 96-99%), and aluminumisopropoxide (C₉H₂₁AlO₃, 98-99%) were purchased from Sigma-Aldrich Co.LLC., Honeywell Riedel-de Haen International Inc., and Acros Organics,USA, respectively, and were used without further treatment. A wide rangeultrasonic atomizing nozzle with an operating; frequency of 20 kHz wasbought from Sonaer Inc., USA.

2. Method of Synthesizing Aluminum Oxide Impregnated Multi-Walled CarbonNanotubes

FIG. 4 shows the vertical chemical vapor deposition (CVD) reactor usedto synthesize aluminum oxide impregnated multi-walled carbon nanotubes.An electric furnace placed about the reaction zone of the reactor wasused to raise the temperature of the reaction zone to a desired reactiontemperature of 750-900° C. Argon gas was used as a carrier gas andhydrogen gas was used as a support gas. Both gases, as well as a liquidreactant solution, were introduced into the preheating zone of thereactor through an inlet, which was operatively connected to the widerange ultrasonic atomizing nozzle, on the top of the preheating zone ofthe reactor. The liquid reactant solution comprising 1 wt % ferrocene, 1wt % aluminum isopropoxide (AIPO), and 98 wt % p-xylene was prepared ina liquid reactant solution mixer connected to an injection (or syringe)pump via a valve. With the injection pump connected to the inlet of thereactor, the liquid reactant solution was injected into the inlet at aflow rate of 90 mL/h and atomized by the wide range ultrasonic atomizingnozzle connected to the inlet of the reactor to result in an evendistribution of the liquid reactant solution inside the reactor as shownin FIG. 2.

The ratio of the carrier gas to the support gas may be varied dependingon specific reaction conditions (e.g. the amount of additional hydrogengas produced from the vaporized liquid reactant solution during the CVDreaction) and the desired characteristics of the reaction product, suchas the length and diameter of the carbon nanotubes that are in partaffected by the catalyst activity protected by the hydrogen gas as areductant. After passing through the reactor, the excess carrier andsupport gases and the vaporized liquid reactant solution, and gaseousreaction waste products exit the reactor via an outlet at the bottom ofthe cooling zone.

The CVD reaction temperature of the reactor was set to 750-900° C.,preferably 850° C. At this high temperature, AIPO was cracked to produceAl₂O₃ according to the following chemical reaction:Al(OCH(CH₃)₂)₃→0.5Al₂O₃+3C₃H₆+1.5H₂O

With ferrocene as the catalyst, C₃H₆ and other carbon source compoundssupplied from p-xylene and ferrocene led to the formation ofmulti-walled carbon nanotubes. The in-situ synthesized alumina particleswere incorporated into or on a surface of the multi-walled carbonnanotubes to form aluminum oxide impregnated multi-walled carbonnanotubes. The flow rates of the hydrogen and argon gases were set to3000 and 1000 sccm, respectively. Deposition of carbon nanotubes on thequartz wall of the reactor was observed. Following the completion of theinjection of the liquid reactant solution, the hydrogen gas flow and theelectric furnace were turned off to allow the reactor to cool down toroom temperature in an argon atmosphere. The aluminum oxide impregnatedmulti-walled carbon nanotubes were separated from the wall of thereactor with a scraper or a brush and collected in the collector at thebottom of the reactor.

Example 2 Characterization of the Synthesized Aluminum Oxide ImpregnatedMulti-Walled Carbon Nanotubes

The synthesized aluminum oxide impregnated multi-walled carbon nanotubeswere characterized and compared with pure multi-walled carbon nanotubesby using scanning electron microscopy (SEM, TESCAN MIRA 3 FEG-SEM),transmission electron microscopy (TEM, field emission electronmicroscope JEM-2100F), energy-dispersive X-ray spectroscopy (EDS), theBrunauer-Emmett-Teller (BET) method to determine the surface areas(Quantachrome, Autosorb IQM0000-4), and X-ray diffraction (XRD) (DesktopX-ray Diffractometer, Miniflex II).

Dispersion of Al₂O₃ on the surface of the multi-walled carbon nanotubescould be varied by changing the reaction parameters that affected theimpregnation process. Comparing FIG. 6, which is an SEM image of thealuminum oxide impregnated multi-walled carbon nanotubes, with FIG. 5,which is an SEM image of pure multi-walled carbon nanotubes, thealuminum oxide impregnated multi-walled carbon nanotubes had cloudyparticles present on the surface of the multi-walled carbon nanotubes.Comparing FIG. 8, which is a TEM image of the aluminum oxide impregnatedmulti-walled carbon nanotubes with the arrows pointing to the cloudyparticles covering the surface of the multi-walled carbon nanotubes,with FIG. 7, which is a TEM image of the pure multi-walled carbonnanotubes, the TEM analysis showed in greater detail the structure ofthe aluminum oxide impregnated multi-walled carbon nanotubes and thepure multi-walled carbon nanotubes

EDS measurement was used to determine the exact atomic weight percent ofthe elements present in the aluminum oxide impregnated multi-walledcarbon nanotubes, with the results presented in FIG. 9A and FIG. 9B. Thebuilding block of carbon nanotubes, carbon was present at about 67.8% ofthe total weight of the aluminum oxide impregnated multi-walled carbonnanotubes. The catalyst for the growth of the multi-walled carbonnanotubes, iron was present at about 8.2% of the total weight of thealuminum oxide impregnated multi-walled carbon nanotubes. Aluminum andoxygen were present at about 11.2% and about 12.9% of the total weightof the aluminum oxide impregnated multi-walled carbon nanotubes,respectively. However, the stoichiometric ratio of aluminum to oxygenwas not 2 to 3 as expected in Al₂O₃.

XRD analysis was used to identify the atomic and molecular structure ofaluminum and oxygen present in the synthesized aluminum oxideimpregnated multi-walled carbon nanotube sample, with the resultspresented in FIG. 10. Different peaks were obtained based on regularityand symmetry of the sample. One main peak at 2 θ=25.88 shows thepresence of multi-walled carbon nanotubes. Other low intensity peaksrepresent the presence of oxides of aluminum. The phase and molecularforms of the elements present in the sample were determined by abuilt-in peak fitting technique of the XRD instrument. Referring to FIG.10, aluminum and oxygen were present in the sample at different Al to Oratios. Mostly Al₂O₃ in corundum phase was present in the sample, butnon-stoichiometnc alumina phase Al_(2.667)O₄ was also present. The newphase of alumina accounts for the unexpected stoichiometric ratio ofaluminum to oxygen obtained from the EDS analysis, and may be the resultof a side reaction taking place in the reactor or due to an incompletecrystallization process.

The surface areas of the pure multi-walled carbon nanotubes and thealuminum oxide impregnated multi-walled carbon nanotubes were measuredby using BET nitrogen adsorption at a temperature of 77 K. The resultsshowed that the surface area of the pure multi-walled carbon nanotubeswas 100 m²/g, whereas that of the aluminum oxide impregnatedmulti-walled carbon nanotubes was 820 m²/g. The increased surface areaof the aluminum oxide impregnated multi-walled carbon nanotubes mayresult from an even distribution of the aluminum oxide particles on thesurface of the multi-walled carbon nanotubes.

The invention claimed is:
 1. A vertical chemical vapor depositionreactor, comprising: a preheating zone portion; a preheating elementinterposed between a top and bottom of the preheating zone portion thatdefines the preheating zone portion, wherein the preheating element isconfigured to heat the preheating zone portion to a preheatingtemperature; a first inlet located at the top of the preheating zoneportion and an ultrasonic atomizing nozzle operatively connected to thefirst inlet configured to release carrier, support, and/or reactantgases and at least one liquid reactant solution into the preheating zoneportion; a reaction zone portion located below the preheating zoneportion; a heater interposed between a top and a bottom of the reactionzone portion that defines the reaction zone portion, wherein the heateris configured to heat the carrier, support, and/or reactant gases andthe at least one liquid reactant solution to a reaction temperature thatis higher than the preheating temperature; a cooling zone portionlocated below the reaction zone portion; and a product collector locatedbelow the cooling zone portion configured to collect a solid chemicalvapor deposition reaction product; wherein the preheating zone portion,the reaction zone portion, the cooling zone portion, and the productcollector are fluidly connected.
 2. The vertical chemical vapordeposition reactor of claim 1, wherein the product collector isremovably attached to a bottom of the cooling zone portion.
 3. Thevertical chemical vapor deposition reactor of claim 1, wherein thepreheating zone portion, the reaction zone portion, and the cooling zoneportion are cylindrically shaped, and wherein a diameter of the reactionzone portion is larger than a diameter of the preheating zone portion.4. The vertical chemical vapor deposition reactor of claim 1, whereinthe preheating zone portion, the reaction zone portion, and the coolingzone portion are cylindrically shaped, and wherein a diameter of thereaction zone portion is larger than a diameter of the preheating zoneportion and the cooling zone portion.
 5. The vertical chemical vapordeposition reactor of claim 1, wherein the first inlet is operativelyconnected to a pump that is connected to a liquid reactant solutioncontainer or mixer.
 6. The vertical chemical vapor deposition reactor ofclaim 1, further comprising an outlet located at a bottom of the coolingzone portion configured to remove at least one reaction waste productfrom the cooling zone portion.
 7. The vertical chemical vapor depositionreactor of claim 6, further comprising a second inlet located at the topof the preheating zone portion configured to introduce an evacuation gasinto the preheating zone portion to displace and remove the at least onereaction waste product.
 8. The vertical chemical vapor depositionreactor of claim 1, wherein the preheating element is disposed outsideof the preheating zone portion.
 9. The vertical chemical vapordeposition reactor of claim 1, wherein the heater is disposed outside ofthe reaction zone portion.
 10. The vertical chemical vapor depositionreactor of claim 1, further comprising insulation disposed outside andaround the preheating zone portion, the reaction zone portion, and thecooling zone portion.
 11. The vertical chemical vapor deposition reactorof claim 10, wherein the insulation is graphite foam or quartz wool.